Filling-enforced Kondo semimetals in two-dimensional non-symmorphic crystals

We study the competition between Kondo screening and frustrated magnetism on the non-symmorphic Shastry-Sutherland Kondo lattice at a filling of two conduction electrons per unit cell. A previous analysis of this model identified a set of gapless partially Kondo screened phases intermediate between the Kondo-destroyed paramagnet and the heavy Fermi liquid. Based on crystal symmetries, we argue that (i)~both the paramagnet and the heavy Fermi liquid are {\it semimetals} protected by a glide symmetry; and (ii)~partial Kondo screening breaks the symmetry, removing this protection and allowing the partially-Kondo-screened phase to be deformed into a Kondo insulator via a Lifshitz transition. We confirm these results using large-$N$ mean field theory and then use non-perturbative arguments to derive a generalized Luttinger sum rule constraining the phase structure of 2D non-symmorphic Kondo lattices beyond the mean-field limit.